Test GL_LINES_ADJACENCY, GL_LINE_STRIP_ADJACENCY, GL_TRIANGLES_ADJACENCY
and GL_TRIANGLE_STRIP_ADJACENCY primitive rendering with several options:
- First and last provoking vertex
- Front and back-face culling
- glPolygonMode(GL_FRONT_AND_BACK, GL_LINE)

There's also a "ref" (reference) option that draws the primitive in
terms of regular lines/triangles so that the "extra" lines/triangles in
an adjacency primitive are displayed.

v2: call glBindAttribLocation() for "vertex" and "color", plus minor
clean-ups.

Signed-off-by: Brian Paul <brianp@vmware.com>